Apex domains cannot have CNAME records.
Question and response
Question
dig sws.cz. NS
Answer
sws.cz. 5 NS ns.sws.cz.
sws.cz. 5 NS ns.profik.cz.
sws.cz. 5 NS ns.profik.net.
Authority
The response has no authority records.
Additional
ns.sws.cz. 5 A 194.228.54.34
ns.profik.cz. 5 A 212.24.149.133
ns.profik.net. 5 A 62.44.3.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0